This invention relates generally to magnetically coupled pumps, known as a "sealless pump" and more particularly to the use of pumped liquid to lubricate the bearings and to cool the area surrounding the magnets.
A sealless pump is a type of centrifugal pump that has its impeller and bearing system isolated from the impeller driving mechanism by an isolating wall or shell that seals the pumping mechanism from the surrounding environment and eliminates the necessity to use rotary seals to seal the pumped fluid against leaking along the shaft. This type of pump is particularly desirable when pumping environmentally sensitive fluids such as hydrocarbons. The driving mechanism is coupled to the pump impeller by an arrangement of magnets located on the opposite sides of the isolating wall which magnetically connects the torque of the driving mechanism to the impeller.
The magnetically coupled pump designs produced today use the pumped liquid to lubricate the bearings and to cool the area surrounding the magnets. Cooling of the magnet area is required because eddy current losses in metallic primary containment shells generate heat. The amount of heat generated by the eddy current losses is a function of the containment shell material and thickness, with nonmetallic shells eliminating these losses. Approximately one-half of this heat is transferred from the shell by convection to the pumpage circulated through the magnet area.
Internal circulation is typically either from discharge to discharge pressure, utilizing an internal pumping device, or from discharge to suction pressure, where, because of the heat acquired by the circulating flow, problems with flashing in the magnet area or in the impeller inlet may occur.
The foregoing illustrates limitations known to exist in present magnetically coupled centrifugal pumps. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.